[python]signal

• signal包的核心是使用signal.signal()函数来预设(register)信号处理函数，singnal.signal(signalnum, handler)

def spawn_visdom():
    try:
        subprocess.run(["visdom  > visdom.txt 2>&1 &"], shell=True)
    except:
        print("Visdom is already running...")

    def signal_handler(signal, frame):
        subprocess.run(["pkill visdom"], shell=True)
        print("Killing Visdom server...")
        sys.exit(0)

    signal.signal(signal.SIGINT, signal_handler)

• 利用alarm制作一个超时器，该示例实现的功能是，为了防止打开一个文件出错或者其他异常一直处于等待的状态，设定一个定时器，5秒后触发IOError。如果5s内正常打开文件，则清除定时器。

import signal, os

# 定义一个信号处理函数，该函数打印收到的信号，然后raise IOError
def handler(signum, frame):
    print 'Signal handler called with signal', signum
    raise IOError("Couldn't open device!")

# 对SIGALRM(终止)设置处理的handler, 然后设置定时器，5秒后触发SIGALRM信号
signal.signal(signal.SIGALRM, handler)
signal.alarm(5)

# This open() may hang indefinitely
fd = os.open('/dev/ttyS0', os.O_RDWR)
signal.alarm(0)          # 关闭定时器